Recently, for meeting the demand for a higher recording density in a magnetic storage system, thin-film magnetic heads have been used in increasing numbers, as compared to the bulk type magnetic heads, because of the possibility of size reduction and the superior high frequency characteristics proper to the thin-film magnetic heads.
Referring to FIG. 1, showing the electro-magnetic transducer section of the thin-film magnetic head, except the protective layer, in a plan view, the electro-magnetic transducer section of the thin-film magnetic head includes a magnetic or non-magnetic substrate 1, on which there are formed upper and lower magnetic layers 2 and 6, formed of sendust or amorphous metal, a coil conductor layer 4 of an electrically conductive material, such as Cu, formed by a coil 4a and pads 4b, and an insulating layer of an organic or inorganic material, by conventional film-forming means and fine processing means. A protective layer for mechanically protecting the thin-film magnetic head is formed ultimately for overlying these separate layers.
With the above described electro-magnetic transducer device, signals are transmitted or received between a magnetic gap 9 formed at the distal ends of the upper and lower magnetic films 2 and 6 and a magnetic recording medium, so as to be transmitted and received between the upper and lower magnetic films and the coil 4a and to the pads or terminals 4b connected integrally to the coil 4a. The signals are ultimately transmitted between the pads 4b and an external electronic circuit, not shown.
In the conventional thin-film magnetic heads, the pad portions 4b connected integrally to the coil 4a and functioning as a connection to an external circuitry are once covered in their entirety by the protective layer functioning as the ultimate layer and are subjected to subsequent removal of the protective layer by etching. The etching methods utilized may include, for example, an ion beam etching by an argon gas, a dry etching by reactive etching by a flon based gas, and a wet etching by hydrofluoric acid. There is also proposed a method according to which formation of a thick protective layer is inhibited by a mask and only a portion of the protective layer which cannot be inhibited by the mask is removed by wet etching using hydrofluoric acid.
In addition, the technology of forming a metal layer on a substrate in accordance with a predetermined pattern in the field of thin-film magnetic heads and other electronic devices has received much recent attention. Hence, various attempts have been made for improving the technology.
Referring to FIGS. 3(A) to 3(D), the conventional method for forming the metal pattern is explained with reference to the method for forming a conductor pattern by a lift-off method using a photoresist which is employed in the thin-film magnetic head.
On a substrate 111, the surface of which has been finished to a smooth mirror surface, an insulating layer 112, a first resist layer 113 and a second resist layer 114 are formed step by step. The first and second resist layers 113 and 114 are formed of organic resist materials having different etching rates. Alternatively, only an upper region of the first resist layer may be treated with a suitable chemical to form the second resist layer. This process step is shown at (A) in FIG. 3.
The first and second resist layers 113 and 114 are then selectively removed by etching to form a pattern groove 116 and an exposed surface 112A of the insulating layer 112 on the groove bottom. At this time, the first resist layer 113 is undercut, by taking advantage of the differential etching rates between the first and second resist layers, for forming an overhang 114A in the second resist layer 114 for facilitating the lift-off. This process step is shown at (B) in FIG. 3.
A conductor layer 115 is then formed by a vapor deposition technique like sputtering or vacuum deposition. The conductor layer 115 is formed on the surface of the second resist layer 114 and on the pattern grooves 116 on the exposed surface 112A of the insulating layer 112. The portions of the conductor layer 115 formed on the unetched second resist layer 114 and in the grooves 116, the remaining second resist layer 114 and the unetched first resist layer 113 are then removed step by step by using a suitable etchant, so that a fine metallic pattern composed of the unetched conductor layer 115 is ultimately left on the insulating layer 112 disposed on the substrate 111. Subsequently, another insulating layer is formed in each gap defined between the turns of the conductor layer 115 so that the upper surface of the conductor layer 115 and the upper surface of the distinct insulating layer formed in the gaps will form a continuous flat surface (not shown).
Thus, in a thin-film magnetic head, as recently developed, layer constituting a magnetic head, namely, a lower magnetic layer, a coil conductor layer and an upper magnetic layer, as well as insulating layers interposed between these layers, can be formed by a thin film forming technique, such as sputtering. Thus, a magnetic head superior in mass producibility and uniform in characteristics may be obtained. Also, since patterning is carried out by the photo-lithographic method, it becomes possible to reduce the width of, for example, the recording track or the magnetic gap. Thus, with the above described conventional thin-film magnetic head, the magnetic field taking part in recording becomes steep to enable recording with a high recording density and high resolution, as well as reduction of the size of the magnetic head.
However, with the conventional thin-film magnetic head, it is difficult to increase the number of turns of the coil conductor layers, by reason of its structural constraints, such that, for raising the recording efficiency of the magnetic head, it becomes necessary to reduce the amount of the depth of the magnetic gap to an extremely small value in an order of 10 .mu.m.
Hence, it is crucial with this type of magnetic head to control the amount of the depth to a predetermined value with high accuracy.
In the conventional practice, shown in FIG. 8, a marker 204' in the form of, for example, a right-angled isosceles triangle for detecting the amount of the depth of the magnetic gap is formed in the thin film magnetic head, and the width l of the marker is measured at a facing surface of the magnetic head adapted to face a magnetic recording medium, referred to hereinafter as "facing surface". The amount of the depth is calculated from the measured value of the width l by mathematical conversion, thereby controlling the amount of the depth.
The marker is formed simultaneously with the coil conductor layer in the vicinity of the magnetic gap by a photo-lithographic technology.
However, the marker in the form of the right-angled isosceles triangle shown in FIG. 8 tends to be deviated from the ideal designed contour shown by a broken line in FIG. 9 due to inaccuracies in resist patterning, marker etching, etc., as a result of which an error (.DELTA.L+.DELTA.L') may be produced in the marker width on the facing surface to render it difficult to detect the amount of the depth accurately. Heating after application of a resist pattern layer through a mask is necessary to cause the applied resist to flow in order to round the edge to eliminate stepping which would otherwise cause microcracks due to insufficient step coverage in an overlaid layer at the pattern edge step. This heating entails changes in the marker pattern.